At a Glance

Why Get Tested?

When to Get Tested?

When your doctor thinks that you may have a problem affecting the function of your kidneys, such as an obstruction within the kidney or acute or chronic kidney failure, or dysfunction due to another disease, such as congestive heart failure

Sample Required?

Test Preparation Needed?

None

The Test Sample

What is being tested?

This test measures creatinine levels in both a sample of blood and a sample of urine from a 24-hour urine collection. The results are used to calculate the amount of creatinine that has been cleared from the blood and passed into the urine. This calculation allows for a general evaluation of the amount of blood that is being filtered by the kidneys in a 24-hour time period.

Creatinine is a waste product produced in the muscles from the breakdown of a compound called creatine. Creatine is part of the cycle that produces energy needed to contract muscles. The amount of creatinine produced in the body is dependent on muscle mass and is relatively constant for an individual.

Almost all creatinine is removed from the body by the kidneys, so levels in the blood are a good indication of how well the filtering units in the kidneys, called glomeruli, are functioning. The amount of creatinine removed from the blood depends on both the filtering ability of the glomeruli in the kidneys and the rate at which blood is carried to the kidneys.

The amount of blood filtered per minute is known as the Glomerular Filtration Rate (GFR). If the glomeruli are damaged or diseased, or if blood circulation is slowed, then less creatinine will be removed from the blood and released into the urine and the GFR will be decreased.

There are several versions of the creatinine clearance calculation. All of them include the measurement of the amount of creatinine in a blood sample collected just before or after the urine collection, the amount of creatinine in 24-hour urine sample, and the 24-hour urine volume. Since the amount of creatinine produced depends on muscle mass, some calculations also use a correction factor that takes into account a person's body surface area (using their height and weight).

How is the sample collected for testing?

The test requires a 24-hour urine collection and a blood sample drawn either at the beginning or end of the urine collection. The blood sample is drawn by needle from a vein in the arm. The person being tested will also usually be asked to provide their current height and weight.

Is any test preparation needed to ensure the quality of the sample?

The Test

How is it used?

A creatinine clearance test is used to help evaluate the rate and efficiency of kidney filtration. It is used to help detect and diagnose kidney dysfunction and/or the presence of decreased blood flow to the kidneys.

In people with known chronickidney disease or congestive heart failure (which decreases the rate of blood flow), the creatinine clearance test may be ordered to help monitor the progress of the disease and evaluate its severity. It may also be used to help determine if and when kidney dialysis may be necessary.

When is it ordered?

The creatinine clearance test may be ordered whenever a doctor wants to evaluate the filtration ability of the kidneys. It may be ordered as follow up when a person has, for example, increased blood creatinine concentrations on a routine CMP or protein in the urine on a routine urinalysis. It may be ordered when there is a suspected kidney disorder because of certain signs and symptoms.

Signs and symptoms that may be an indication of kidney problems include:

Swelling or puffiness, particularly around the eyes or in the face, wrists, abdomen, thighs, or ankles

Urine that is foamy, bloody, or coffee-colored

A decrease in the amount of urine

Problems urinating, such as a burning feeling or abnormal discharge during urination, or a change in the frequency of urination, especially at night

Mid-back pain (flank), below the ribs, near where the kidneys are located

High blood pressure

Blood and/or protein in the urine

It may also be ordered periodically when it is known that someone has a kidney disorder or decreased blood flow to the kidneys due to a condition such as congestive heart failure.

What does the test result mean?

Any disease or condition that affects the glomeruli can decrease the kidneys' ability to clear creatinine and other wastes out of the blood. When this occurs, the blood creatinine level will be increased and the creatinine clearance will be decreased because not as much creatinine is able to be excreted in the urine. A number of diseases and conditions can affect kidney function. For more on these, see Kidney and Urinary Tract Function, Disorders, and Diseases.

1. Why do I have to collect my urine for 24 hours?

A 24-hour urine sample is required instead of a random urine sample because the amount of creatinine in the urine will vary somewhat during the course of a day. By collecting all urine for 24 hours, the amount of creatinine in the urine can be averaged over the entire day and will give a better indication of what is going on in the body.

2. What should I do if I forget to save one urine sample during the collection?

If you do not have a complete collection, the results will not be valid. You should call your doctor's office or the laboratory where you obtained your collection container to ask if you should discontinue the test and begin again another day.

3. Are there other ways to estimate or determine the Glomerular Filtration Rate (GFR) of my kidneys?

Yes. The GFR can be estimated using the result of a blood creatinine test and a calculation. (See the article on eGFR). Collection of a 24-hour urine specimen can be prone to errors. A reasonable estimate of actual GFR can be calculated based on serum creatinine, a common test that is easily performed.

Also, there are other, more involved tests that have higher accuracy than a creatinine clearance. However, these involve injecting the patient with a tracer and are more expensive. For most clinical purposes, the accuracy of creatinine clearance is sufficient.

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Article Sources

NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

(Updated 2012 March 23). The Kidneys and How They Work. National Kidney and Urologic Diseases Information Clearinghouse (NKUDIC) [On-line information]. Available online at http://kidney.niddk.nih.gov/kudiseases/pubs/yourkidneys/ through http://kidney.niddk.nih.gov. Accessed November 2012.

(February 2009) National Kidney and Urologic Diseases Information Clearinghouse. The Kidneys and How they Work. Available online at http://kidney.niddk.nih.gov/kudiseases/pubs/yourkidneys/index.htm#tests through http://kidney.niddk.nih.gov. Accessed September 2009.

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This article was last reviewed on November 29, 2012. | This article was last modified on November 29, 2012.

The review date indicates when the article was last reviewed from beginning to end to ensure that it reflects the most current science. A review may not require any modifications to the article, so the two dates may not always agree.

The modified date indicates that one or more changes were made to the article. Such changes may or may not result from a full review of the article, so the two dates may not always agree.